This invention relates to a feedthrough across a solid wall, and, more particularly, to a thermal feedthrough for a solid conductor.
A feedthrough is a structure that permits the selective transmission of a flow of energy or mass through a solid wall. Various types of devices must operate in isolation from temperatures and particular environments. Such devices are normally placed within a sealed enclosure for their operation. However, it often is necessary to selectively transfer some types of energy or mass across the walls of the enclosure, at the same time that the walls prevent the transmission of other types of energy or mass.
As an example, some types of electronic devices must be operated at very low, cryogenic temperatures in a vacuum. The devices are placed into a sealed, insulated enclosure that insulates against a heat flow in to the enclosure and thence to the devices. The interior of the insulated enclosure is evacuated by a vacuum pump either continuously, or initially and then sealed. With such an insulated enclosure, it is usually necessary to provide for two types of feedthroughs in the wall of the insulated enclosure. One is an electrical signal feedthrough, so that electronic signals and sometimes power can be transmitted into and out of the enclosure. Various types of electrical feedthroughs are well known in the art.
The other type of feedthrough is a thermal feedthrough. A thermal feedthrough permits a flow of heat to be removed from within the evacuated space interior to the insulated enclosure to an exterior cooling device, to keep the devices within the insulated enclosure cooled to their operating temperatures. In one possible type of thermal feedthrough, a solid conductor extends from the interior of the insulated enclosure to the exterior, and must pass through the wall of the enclosure.
Such solid conductor thermal feedthroughs are more difficult to construct than electrical feedthroughs, particularly if a vacuum seal must be maintained across the wall and the feedthrough. The problem arises from the fact that the various components of the wall and the feedthrough structures generally have different thermal expansion coefficients. The solid conductor is a metal of high thermal conductivity such as copper, aluminum, or silver. The wall is typically a nonmetallic structure such as fiberglass-reinforced plastic composite material, or a metal structure of low thermal conductivity.
When the interior of the insulated enclosure is cooled, the various components contract at different rates. The components tend to separate from each other as a result of the differing contractions, resulting in vacuum leaks across the feedthrough. The problem is aggravated if the insulated enclosure and the feedthrough are repeatedly cooled and heated, as often occurs during cycles of operation, because some portions of the damage induced by the thermal expansion differences can accumulate with increasing numbers of cycles. The result is an accumulation of thermal fatigue damage to the structure and its eventual failure.
There is a need for an improved approach to solid conductor thermal feedthroughs, which permit efficient heat flow but are resistant to damage such as vacuum leaks induced by single or multiple thermal excursions. The present invention fulfills this need, and further provides related advantages.